Outline

Objective: Lateral mass fusion has become standard in the treatment of cervical spine instability. However the argument that the biomechanical load of the relative short screws compared to pedicle screws is attenuated, persists. Unicortical screws would reduce the risk of injury to adjacent neurovascular structures whereas bicortical fixation provides the required stability. We investigated the screw placement after lateral mass instrumentation of the cervical spine considering soft tissue injury and screw length.

Methods: We analyzed clinical and radiological data from fifty-five consecutive patients who received lateral mass fixation of the cervical spine. To explore whether bicortical placement of screws produces relevant affection of neurovascular structures postoperative CT scans and neurological examination were performed. At the CT-workstation, lateral mass screw length and position (unicortical vs. bicortical) at the levels C3 to C7 were investigated.

Results: All patients received instrumentations with a lateral mass screw and rod system (284 screws) in various levels of the subaxial cervical spine. 235 (82.7%) screws showed bicortical position, whereas the mean missing distance in unicortical screws to bicortical placement was 3.1 mm increasing from the C3- to C7-segment. Median screw length was 16 mm (175 screws, range 12–20 mm). There was no vertebral artery injury, three screws (1.1%) reached into the intervertebral foramen with one screw (0.4%) causing C5 nerve root affection needing revision surgery.